1. Field of Art
The present invention relates to a shrouded rotating wing having an opening of a size exceeding a radius of approximately 3 m and operating based on the principle of a linear motor driving.
2. Background Art
The mechanism of coupling output from a prime mover, such as a turbine positioned near the center of a rotating wing, to a central driving shaft for rotation of the blades, thereby obtaining lift or thrust, has heretofore been used frequently in helicopters and other rotorcrafts. However, the method of making a rotating wing rotate around a shaft defining the central axis of rotation requires a vast amount of energy and thus the efficiency has been low.
Japanese “Kokai” (laid-open application publications) 2001-097288 and H07-205897 disclose a shrouded rotating wing for use as a tail rotor of a single rotor type helicopter. This shrouded rotating wing can rotate blades efficiently and change the rotational speed freely by making a change from the conventional method of transferring power to the central shaft of rotation to a method of generating a driving force at the wing tips.
Kokai H07-205897 discloses a driving method based on a linear motor principle using shroud-side magnets and wing-tip magnets as means for generating a driving force at wing tips. As disclosed therein, the wing-tip magnets may be fitted into the shroud or allowed to float within a space near the shroud-side magnets. In one embodiment wherein the wing tip magnets are fitted into the shroud, neither a rotary shaft nor a hub for connecting the wing center portions of rotor blades is used and, in another such embodiment, the rotor blades are connected to a rotary shaft. However, if the wing tip magnets are fitted into the shroud and neither a rotary shaft nor a hub is used, when the shrouded rotating wing is of a large caliber and is used in a horizontal position, blades tend to fall off due to their own weight and the rotating wing cannot withstand a sudden change of direction. In the type using a rotary shaft to which the rotor blades are connected, no consideration is given to expansion and contraction of the rotor blades, so when the wing caliber is large, the wing tips fitted in the shroud are pulled strongly toward the center due to the weight of the rotor blades, e.g. at the time of parking, resulting in an increase in resistance to rotation. Even if the rotating wing can start to begin rotating, there is a great possibility that the rotating wing will become unrotatable because no consideration is given to expansion and contraction due to centrifugal force or heat. In the type wherein the wing tips are allowed to float near the intra-shroud magnets, due to deflection or distortion of the rotor blades during parking, the wing-tip magnets tend to fall and the gap between the intra-shroud magnets and the wing-tip magnets increases, making the generation of a driving force impossible. Thus, a shrouded rotating wing having a small radius of about 50 to 60 cm is practical when used in the vertical position, that is, when used as a tail rotor of a single rotor type, but it is very difficult to use a shrouded rotating wing of a large caliber in a horizontal orientation or where the blow-off direction is changed rapidly such as that in Japanese Patent Application 2003-290873.
In Japanese Kokai 2001-097288, the principle of an electric motor (basically the same as the principle of a linear motor) is enlarged by mounting a rectifier on a rotary shaft whereby an electric current converted to an alternating voltage by the rectifier is conducted from the wing tips onto a ring, through the rotor blades, to energize electromagnetic coils including an iron core which are embedded in the ring, thereby affording a driving force. Therefore, the ring and the blade tips are fixed together, and when the blades expand or contract to a larger extent than the estimated 3˜5 mm, the operation of the rotating wing becomes difficult. Besides, since the coils through which an electric current flows to generate a magnetic force are embedded together with an iron core into the ring, it is presumed that the ring itself will produce heat. When these influences are taken into account, even if the rotating wing is used in a vertical position as illustrated in the drawings of Kokai 2001-097288, the diameter of 1 to 1.2 m (radius 50˜60 cm) estimated by the inventor is considered to be the limit for size capable of being manufactured.
As reported in Japanese Patent Application 2002-383031 and Kokai 2001-097288, the length of each rotor blade changes due to centrifugal force or a change in temperature. When the rotating wing is about 0.5 to 0.6 m (50 to 60 cm) in radius and is used in a vertical position, as a tail rotor (Kokai 2001-097288 and H07-205897), a change in length, even when estimated to be maximum, is about 0.6% of the rotor blade length, i.e., 0.003 to 0.004 m (3 to 4 mm). Thus, the change is within the single digit range of millimeters and therefore can be absorbed by an outer projection or the like of the ring as in Kokai 2001-097288. However, when the rotating wing is used horizontally as a main rotor, the influence of deflection or distortion of the rotor blades is added to that of the centrifugal force and the temperature change, and during parking, a decrease in projection radius of about 2% is observed in the direction opposite to the direction of the centrifugal force. When the radius of the main motor is 5 m, the expansion caused by centrifugal force, for example, is about 0.03 m (3 cm) and the decrease in projection radius due to deflection or distortion is as large as about 0.1 m (10 cm), with the total being 0.13 m (13 cm) which is on the order of ten-odd centimeters. Thus, in the methods disclosed in Kokai 2001-097288 and H07-205897, it is extremely difficult to maintain an appropriate gap between the magnets which create the driving force and it has so far been impossible to adopt the method disclosed in Japanese Patent Application 2003-290873.
In Japanese application 2002-383031, in order to absorb deflection and distortion of the rotor blades which can cause a change in radius of gyration reaching ten-odd centimeters, and to thereby keep the gap between the shroud-side magnets and the rotor blade wing-tip magnets at an appropriate value, allowing the linear motor driving principle to be exhibited in a stable manner, an electromechanical device is installed within each rotor blade. However, the weight of the rotor blades is increased and the structure is complicated, resulting in an increase in the number of parts and fear of an increase in the number of failure generating factors. Moreover, the wing tips are each independent, so when a load is imposed on a certain specific rotor blade, the dispersion of the load is insufficient and the load of its wing tip imposed on the shroud becomes large. Particularly, when the rotating wing is put on a single-shaft turntable and attached to a flying body as in Japanese Patent Application 2003-290873, abnormal forces are generated against the shroud at two positions, one of which is the nearest to and the other remotest from a side wall of the flying body, by a gyro effect. Even if such portions are strengthened, the service life may be extremely shortened or the portions in question may be damaged.
A shrouded rotating wing based on the driving principle of a linear motor or a shrouded rotating wing based on the principle of an electric motor is simple in structure and light in weight when it is of a small caliber and is used vertically. However, when a shrouded rotating wing of a large caliber is used horizontally, it may become difficult keep an appropriate gap between the driving force generating electromagnets and permanent magnets, due to deflection or distortion induced by centrifugal force, heat, or due to the weight of its rotor blades, or the rotation of the rotatable portion may become difficult due to compression caused by expansion or contraction of its rotor blades, for example. Further, if an attempt is made to keep the gap between electromagnets and permanent magnets appropriate with use of an electromechanical device, not only does the structure become complicated, but also the weight of rotor blades, etc. is increased. Although there is no problem when a shrouded rotating wing is used without a sudden change in direction, in the case of a large caliber used in a horizontal direction, a strong force based on a gyro effect is developed against the shroud if the direction is changed suddenly.